High speed trim with flaps down, 737
 

When you lower the flaps on the 737 the trim motor gives you a higher trim speed. If this is not working correctly, ie slow trim with the flaps down, is this a go or a no go item? I could not find any reference to this problem in the MEL, also the engineer looked puzzled.

... the trim motor gives you a higher trim speed

I'm really quite confused .. what does the trim motor have to do with trim speed ? and why would you want a higher trim speed with greater flap deflection ?

JT - it is the speed of Stab TRIM movement that is referred to (ie 'trimming speed' rather than 'trim speed':) ). Faster with flap extended.

ah ha ! .. thank you, good sir ... jargon can be such a bore at times ..

Not only is it, as ASFKAP mentioned, legally a "No Go" item if it isn't in the MEL, but from an engineering and safety perspective it should be a "No Go" also: you have something wrong with your stab system (whether the motor or the control unit) and that's hardly a trivial system.

The higher trim motor rate when flaps are down/in motion is presumably because it's required, so you may not have the requisite amount of handling. If your aircraft has a flap/stab interconnect, chances are the trim command in response to flap motion is for a number of seconds, not for an actual stab change, so if the rate is wrong, you'll get the wrong amount of stab as a result.

You also don't know if anything else is kaput in the stab system. Inflight would be a bad time to find out.

Hello raspberry,

how did you find out that the high speed trim was not working ? Usually you set the T/O trim unit in the preflight procedure and you have flaps up. Did you recognize the problem in the after landing scan while reseting the trim with flaps not up ?

I recognized the problem in the climb out and on the approach at the other end. As I could not find the problem in the MEL I grounded the aircraft.

I see, and it was the same with the A/P On and Off ?

yes it was the same with the AP switched on.

Ok, thanks for your feedback !:)

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